For many years industry has relied on frequent oil and filter changes to minimize wear and tear on “open” hydraulic systems. The term “open” as used herein refers to systems that include an air breather cap that allows air to enter and leave the oil reservoir due to changes in the level of the oil in the reservoir and air temperature. The “open” oil reservoir operates at near ambient air pressure. The vast majority of hydraulic oil systems and gearboxes are “open” systems.
Some prior art methods have breather caps with filters and/or air driers. These helped reduce ingression contamination but they quickly lose utility because they are costly to service when dirty or the desiccant becomes saturated. Fine particles and moisture are only reduced with this prior art. Still, later prior art methods includes applicants U.S. Pat. No. 4,827,719 that “closed” the “open” system and helped dry the air in the reservoir. This improved contamination control by controlling ingression but all the above prior art failed to prevent oil oxidation. The oil still continues to operate in ambient air concentrations of about 21% oxygen with resultant oxidation of the oil. As oxidation occurs the oil becomes contaminated with detrimental chemicals and the formation of sludge and varnish. The result is continued oil and filter changes as well as wear and tear on seals, valves and internal parts. Systems that require the use of 2 micron or sub-micron oil filters require frequent costly replacements.
The prior art includes the apparatus described in U.S. Pat. Nos. 4,827,719, 4,135,635; 3,330,902; 2,095,752; 1,652,793; and 4,161,964. These devices have not been wholly satisfactory because, in part, they do not reduce the oxygen content thereby allowing oxidation of the oil, sludge formation and oil contamination.
Most hydraulic oil systems are of the “open” system type. They have an oil reservoir with a breather cap. The air space above the oil in the reservoir will typically be 20% or more of the reservoir volume. As the oil level changes due to system operation, or temperature changes reservoir air exits and enters the air breather port to maintain near ambient air pressure. The expansion and contraction of the air and oil along with the system operation causes considerable amounts of air to enter and leave the reservoir. The ambient air entering carries with it 21% oxygen, moisture, dust, dirt, pollen, microbes and many other airborne contaminants. These are all detrimental to oil or other fluid. The expelled air carries with it oil mist that fouls the surrounding equipment with an oil film and contaminants the ambient air with the oil mist. These consequences are all the result of an “open” system.
Typical equipment applications include tractors, automobile braking systems; refuse trucks, military tanks, shipboard, cranes, forklifts, power steering, gearboxes, wind turbines, mining equipment, and food processing plant equipment, hydraulic presses, factories, storage tanks as well as drums and other oil containing equipment. While hydraulic systems are referred to herein those skilled in the art will recognize that apparatus and methods described herein may also be applicable to a wide variety of fluid systems.
Many new automobiles include gear boxes that operate at high speeds and extreme conditions. Such gear boxes function at up to a 300 F operating temperature. Such autos may drive over bumpy roads and run through water that splashes on and quickly cools the gearbox. These sudden temperature changes cause ambient air with water, dirt and other contaminants to enter the air breather port. Such conditions result in costly repairs and downtime and manufacturers then need to charge more and shorten warranty periods. The gearboxes are generally not easily accessible and they will benefit if an oil protection device addresses all the operating conditions whereby no maintenance service will be required for 5 to 10 years.
Many hydraulic systems in both industrial and commercial applications are exposed to substantial environmental related contamination from ambient air and, thus, are highly vulnerable. The major causes for oil contamination are water, ingression of air and airborne contaminants and oxidation of the oil that results in sludge buildup, degradation of the oil and costly service and repairs. For example, garbage trucks commonly have hydraulic system utilizing thirty (30) gallon reservoirs that require frequent oil and filter changes. Despite these changes the systems still suffer repetitive failures of expensive hydraulic equipment and costly downtime. Similar problems occur in numerous other industrial hydraulic systems including automobile brake systems. Frequently the expense of the individual hydraulic system components is very great. In addition, the down time of the equipment involved is also very significant.
Most reservoirs have a breather vent to ambient air. Such systems are considered “open” systems. This process of “reservoir air breathing”, as it is called in industry, is a major source of hydraulic or other fluid contamination. As a result of the sludge from oxidation, dirt and moisture contamination of the hydraulic fluid, the life of all moving parts in the hydraulic system including pumps and various moving apparatus are greatly reduced. In addition, hydraulic fluid and filters must be changed more frequently.
Even systems fitted with inlet breather filters and dryers allow for ingression of air including oxygen as well as moisture and other contaminants. Such filters and dryers help to remove some of the airborne particles and moisture but oxygen, fine particles and moisture still pass through. An additional problem is that many of the dryers become saturated and quickly lose the ability to remove moisture. The exposure of the hydraulic fluid or the lubricant in the reservoir to the ambient atmosphere is undesirable because it results in faster contamination of the lubricant or other hydraulic fluid as well as contamination of the atmosphere when reservoir air is expelled. The contamination of the hydraulic or other fluid is typically caused by oxidation of the fluid which is often accelerated by ambient air entering and leaving the reservoir.
Even “closed” systems are occasionally “open” when fluid is added to the respective system or other service or repair occurs. These prior art devices do nothing to remove the detrimental oxygen in the internal air that results in oxidation of the oil. The ambient air contains 21% oxygen, 78% nitrogen and varying amounts of water vapor. The term “oil” as used herein will be understood to include both oil as well as other fluids including synthetic hydraulic fluids. The oxygen within the reservoir, in the presence of hot oil (operating systems may have fluids that have operating temperatures of 40° F. to 140° F. or more above ambient temperature). Oxidation of the oil occurs, especially during high humid temperatures and this degrades the lubrication qualities resulting in excess wear on metal parts. With even small amounts of moisture in the system the oil contamination occurs.
In the conventional hydraulic system the quantity of fluid in the hydraulic system reservoir can vary substantially during the operating cycle. Various valves may be opened or closed, a cylinder may be full or empty, etc., and, thus the quantity of hydraulic fluid in the reservoir varies substantially during normal operation. In addition, the volumetric expansion rate for the hydraulic fluid and air in the reservoir differs substantially. In the conventional open system, the air breather cap allows air to enter and leave as the respective volumes of hydraulic fluid and air in the reservoir change. For example, the oil level in the reservoir may change only 5 percent due to temperature changes and system operation. However, the air volume above the reservoir may vary 15 percent due to temperature changes. Oil has a coefficient of cubical expansion of 0.0004/degree F. If the oil temperature increased from 60° F. to 140° F. (80° F. temperature difference) it would result in an increase in cubical volume by 3%. Air at 60° F. has a specific volume of 13.2 CF/lb. (cubic feet per pound). Air at 140° F. has a specific volume of 15.4 CF/lb. Therefore, the air increases in volume 16% as the result of the same 80° F. increase. A hydraulic oil reservoir always remains close to ambient pressure, even in “closed” systems. Pressure relief valves insure very little buildup of pressure or vacuum. This results in a 20 percent total volume change. Since the oil remains in the system, the entire 20 percent air volume change passes back and forth through the air breather port drawing in ambient air with all its contaminants.
Oil oxidation is one of the most serious oil contamination problems and cause of frequent oil and filter changes and results in downtime and shortened hydraulic equipment life. Oil oxidation is the chemical reaction that occurs between an oil molecule and oxygen which is present in the ambient air. Ambient air contains 21% oxygen and 78% nitrogen. A nitrogen environment is desired in contact with oil because nitrogen is an inert gas.
Oil oxidation results in a catastrophic and permanent chemical change to the base oil molecules that degrade the oils lubrication properties. When oil oxidation occurs the degraded oil includes detrimental chemicals including aldehydes, ketones, hydro peroxides and carboxylic acids.
The rate at which oil oxidation occurs depends on the temperature and oxygen concentration along with many other factors. Many chemical reactions including rates of oxidation increase exponentially with increasing temperature. The rate of oil oxidation may double for every 10° C. (18° F.) rise in temperature above 75° C. (165° F.). The range of temperatures that hydraulic systems, gear boxes and other oil systems operate varies widely depending on environmental and other factors with below freezing to over 100° C. (212° F.) being not uncommon.
The formation of Carboxylic acids cause acidic corrosion and the formation of sludge and varnish in solid form. Such materials are sticky and can cause filter plugging, fouling of critical oil clearances and valve stiction in hydraulics systems. Water in the oil that mixes with the sludge causing even more corrosion and wear problems.
From the above, it is therefore seen that there exists a need in the art to overcome the deficiencies and limitations described herein and above.
Various other applications such as commercial processes utilizing various fluids will be apparent to those skilled in the art. Examples of application for the present invention include systems utilizing (1) petroleum based lubricants and hydraulic fluids and (2) synthetic fluids including synthetic hydraulic fluids as well as to other fluids and (3) drums and tanks for storage such as fuel tanks.